Sodium storage in a promising MoS2–carbon anode: elucidating structural and interfacial transitions in the intercalation process and conversion reactions

Abstract

Sodium-ion batteries and capacitors are considered as low-cost energy storage devices, compared to Li-ion counterparts. However, most anodes for sodium-ion devices show sluggish kinetics and poor structural stability caused by the large radius (1.02 Å) of Na⁺. One candidate anode is MoS₂, a 2D atomic layered material with a large interlayer spacing of 6.2 Å, that can take up and release Na⁺via two working principles: a two-electron intercalation process and a four-electron conversion reaction. Herein, we report a facile method to synthesize a MoS₂–amorphous carbon (MoS₂–AC) nanocomposite and further study the effect of the two working principles on the structure, interphase, and charge storage properties of MoS₂–AC. The two-electron intercalation reaction enables the MoS₂–AC electrode to have a higher rate capability and superior stability than that via the four-electron Na⁺ conversion reaction. This favorable Na⁺ charge storage performance of MoS₂–AC via the two-electron intercalation process is attributed to its pseudocapacitive behavior, a stable solid electrolyte interphase and robust stability of the structure, which enables us to fabricate a sodium-ion capacitor that can deliver high energy density at a high rate. This work underscores the potential importance of realizing fast Na⁺ charge storage via an intercalation process as a strategy for the fabrication of high-performance sodium-ion capacitors and batteries.